I keep both a spread sheet and a database of cel 
stats including information such as purchase 
price, date, and dealer.  I do this partially for 
good record keeping and partially because it 
entertains me.  I really like to see my cel 
statistics.  So, I can both graph my purchases by 
month or series and check out exactly how many of 
my cels have characters with purple hair ^^;  
It's interesting to see which series average 
higher than others.  I'm still gathering data on 
the exact measurements of my cels and I come up 
with new things to keep track of all the time. 

I also have a short sheet of transactions in the 
past month or two that gives me a quicker idea of 
who I owe, what I'm expecting in and what I've 
recently spent.  Usually I can just remember that 
on my own but it never hurts to double check ^_^.

Keys
*the big number at the bottom is scary*